Highly regular logic design for efficient 3D integration

ABSTRACT

An integrated circuit includes an array of unit cells, each unit cell of which including field effect transistors arranged in a stack. Local interconnect structures form select conductive paths between select terminals of the field effect transistors to define cell circuitry that is confined within each unit cell. An array of contacts is disposed on an accessible surface of the unit cell, where each contact is electrically coupled to a corresponding electrical node of the cell circuitry.

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. § 119(e) from U.S.Provisional Patent Application No. 62/879,721 entitled “Ultra-regularLogic Design for Efficient 3D Integration,” filed Jul. 29, 2019, theentire disclosure of which incorporated herein by reference

BACKGROUND

This disclosure relates to integrated circuits and the fabrication ofmicroelectronic devices.

In the manufacture of a semiconductor device (especially on themicroscopic scale), various fabrication processes are executed such asfilm-forming depositions, etch mask creation, patterning, materialetching and removal, and doping treatments. These processes areperformed repeatedly to form desired semiconductor device elements on asubstrate. Historically, with microfabrication, transistors have beencreated in one plane, with wiring/metallization formed above the activedevice plane, and have thus been characterized as two-dimensional (2D)circuits using 2D fabrication techniques. Scaling efforts have greatlyincreased the number of transistors per unit area in 2D circuits, yetthese scaling efforts are running into greater challenges as scalingenters single digit nanometer semiconductor device fabrication nodes.Semiconductor device fabricators have expressed a desire forthree-dimensional (3D) semiconductor circuits in which transistors arestacked on top of each other.

3D integration (3Di) is seen as a viable option for continuingsemiconductor scaling efforts despite inevitable saturation in criticaldimension scaling. As the contacted gate pitch reaches its scaling limitdue to manufacturing variability and electrostatic limitations,two-dimensional transistor density scaling can go no further. Evenexperimental new transistor designs, such as vertical channel gate allaround transistors, that may one day be able to overcome these contactedgate pitch scaling limits, have scaling issues of their own due toresistance, capacitance, and reliability concerns, thereby limiting thedensity with which transistors can be wired into circuits.

3Di, i.e., the vertical stacking of multiple devices, aims to overcomethese scaling limitations by increasing transistor density in volumerather than area. While this concept has been successfully demonstratedand implemented by the flash memory industry (e.g., 3D NAND), mainstreamcomplementary metal-oxide-semiconductor (CMOS) very large scaleintegration (VLSI) manufacturers of CPU and GPU products remain hesitantto adopt 3D integration as a primary means of moving the semiconductorroadmap forward. The main reason for this lack of adoption of 3Di foranything other than niche applications (e.g., memory stacked on top oflogic for machine learning accelerators used in artificial intelligencechips) is the inherent inefficiency of known proposals.

One approach to successful semiconductor scaling is to leverage a modestincrease in process complexity and cost across a substantially largernumber of transistors. In 2D scaling this was accomplished by reducingfeature size and increasing transistor density at largely fixed wafermanufacturing cost. 3D integration approaches that double transistordensity in volume by incurring twice the manufacturing cost, however, donot offer viable scaling solutions. Successful scaling using 3Di lies inradical reduction of process and design complexity to minimizenode-to-node cost increase.

SUMMARY

An integrated circuit includes an array of unit cells, each unit cell ofwhich including field effect transistors arranged in a stack. Localinterconnect structures form select conductive paths between selectterminals of the field effect transistors to define cell circuitry thatis confined within each unit cell. An array of contacts is disposed onan accessible surface of the unit cell, where each contact iselectrically coupled to a corresponding electrical node of the cellcircuitry.

In an additional or alternative aspect of the inventive conceptdisclosed herein, the integrated circuit includes a functionalizationlayer comprising electrically conductive wiring segments formed betweenselect contacts on the respective accessible surfaces of one or moreunit cells in the array.

In another additional or alternative aspect of the inventive conceptdisclosed herein, the unit cells have a common footprint and arepositioned in the array so that diffusion breaks embracing the cellcircuitry of each unit cell align with the diffusion breaks in adjacentunit cells to form continuous spaces that extend across all unit cellsin respective columns of the array.

In yet another additional or alternative aspect of the inventive conceptdisclosed herein, the integrated circuit includes power walls disposedin the continuous spaces that provide electrical power to at least theunit cells in the respective columns of the array.

In another additional or alternative aspect of the inventive conceptdisclosed herein, upper surfaces of the respective power walls areexposed on the accessible surface of each unit cell in the columns ofthe array.

In yet another additional or alternative aspect of the inventive conceptdisclosed herein, the cell circuitry is the same across all unit cellsin the array.

In another additional or alternative aspect of the inventive conceptdisclosed herein, the cell circuitry is constructed from like frontend-of-line and middle end-of-line processes.

In yet another additional or alternative aspect of the inventive conceptdisclosed herein, the front-end of line and middle-end of line processesinclude multiplication patterning processes.

In another additional or alternative aspect of the inventive conceptdisclosed herein, the multiplication patterning processes includedirected self-assembly and/or self-aligned multiple-exposure patterning.

In yet another additional or alternative aspect of the inventive conceptdisclosed herein, the field effect transistors are stacked incomplementary pairs.

In another additional or alternative aspect of the inventive conceptdisclosed herein, gates of the complementary pairs of field effecttransistors are commonly connected.

In yet another additional or alternative aspect of the inventive conceptdisclosed herein, the complementary pairs in the stack of field effecttransistors is greater than one in number.

It is to be understood that this summary section does not specify everyembodiment and/or incrementally novel aspect of the present disclosureor claimed invention. Instead, this summary only provides a preliminarydiscussion of different embodiments and corresponding points of noveltyover conventional techniques. The Detailed Description section andcorresponding figures of the present disclosure provide additionaldetails and/or possible perspectives of the invention and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a top-down view of an example unit cellwith which the principles of this disclosure can be embodied.

FIG. 2, including FIGS. 2A-2E, is a diagram revealing the internal, 3Dstructure of the example unit cell illustrated in FIG. 1.

FIG. 3A is an illustration of a 10×10 array of unit cells in accordancewith the principles described herein to highlight the regularity of thefront end-of-line (FEOL) and middle end-of-line (MEOL) layouts.

FIG. 3B is an illustration of a unit cell array in which only the activechannel regions and source/drain contacts in accordance with theprinciples described herein are depicted.

FIG. 3C is an illustration of unit cell array in which a grid ofcut-masks in accordance with the principles described herein aredepicted.

FIG. 3D is an illustration of a unit cell array in which VDD power railsand VSS power rails in accordance with the principles described hereinare depicted.

FIG. 4 is an illustration of a top-down view of a unit cell that hasundergone functionalization to form a two-fingered inverter (INV2) logiccell in accordance with the principles described herein.

FIG. 5 is an illustration of a top-down view of a pair of unit cells asfunctionalized into a two input and-or-invert (AOI22) logic cell inaccordance with the principles described herein.

FIG. 6 is an illustration of a top-down view of a pair of unit cells asfunctionalized into a two input and (AND2) logic cell in accordance withthe principles described herein.

FIG. 7 is an illustration of a top-down view of a pair of unit cells,each of which having a single CFET pair in their respective activedevice stacks as opposed to two CFET pairs, functionalized into a twoinput not-and (NAND2) logic cell in accordance with the principlesdescribed herein.

DETAILED DESCRIPTION

The present inventive concept is best described through certainembodiments thereof, which are described in detail herein with referenceto the accompanying drawings, wherein like reference numerals refer tolike features throughout. It is to be understood that the terminvention, when used herein, is intended to connote the inventiveconcept underlying the embodiments described below and not merely theembodiments themselves. It is to be understood further that the generalinventive concept is not limited to the illustrative embodimentsdescribed below and the following descriptions should be read in suchlight.

Additionally, the word exemplary is used herein to mean, “serving as anexample, instance or illustration.” Any embodiment of construction,process, design, technique, etc., designated herein as exemplary is notnecessarily to be construed as preferred or advantageous over other suchembodiments. Particular quality or fitness of the examples indicatedherein as exemplary is neither intended nor should be inferred.

Techniques herein include integrated circuits and methods of fabricationof semiconductor devices that use common front end-of-line and middleend-of-line structures for all logic cells and then functionalize thesegeneric unit cells in low-level metallization. One embodiment includesan integrated circuit having an array of unit cells. Each unit cell mayhave a same unit cell height and a same unit cell width. Each unit cellmay have at least two vertical levels of transistors in which a firstfield effect transistor is positioned above a second field effecttransistor in a stack. Each field effect transistor may have agate-all-around channel. Each unit cell may include local interconnectwiring that electrically connects source/drain and gate structures. Oneor more wiring levels may be positioned directly above the array of unitcells, in which at least two different types of functional logic cellsmay be formed from the array of unit cells. Accordingly, such techniquescan provide 3D integration having process simplification and costreduction.

Techniques herein include those by which integrated circuits arephysically constructed or otherwise realized as a physical object,including techniques by which the integrated circuits are designed andfabricated. Indeed, those having skill in the relevant art(s) and anunderstanding of this disclosure will be able to carry the principlesdescribed herein into suitable electronic/engineering design automation(EDA) and foundry platforms through which the structures describedherein can be physically constructed and/or used as components of abroader circuit design. Techniques herein find particular applicabilityto monolithically integrated 3D CMOS (complementarymetal-oxide-semiconductor) circuits, such as described in U.S.Provisional Patent Application Ser. No. 62/727,097, filed on Sep. 5,2018, entitled, “Architecture Design and Processes for ManufacturingMonolithically Integrated 3D CMOS Logic and Memory,” which isincorporated by reference herein it its entirety.

Functionalization of logic can be carried out as a back end-of-line(BEOL) operation through, for example, metallization over areadily-accessible grid of contacts providing electrical access tointernal circuit components of the three-dimensional unit cell.

Embodiments herein include enforcing a common 2 contacted poly pitch(cpp) footprint on the unit cell width. Although this restriction limitsthe unit cell to a single transistor track flanked on either side bysingle diffusion breaks, this design enables substantial scalingbenefits and facilitates significant complexity reduction. For example,designing all unit cells onto a fixed-width footprint results inalignment of diffusion breaks across all rows of a corresponding logicblock. This arrangement facilitates formation of local power rails thatrun in the unoccupied space of the diffusion break, giving unobstructedaccess to the source regions of devices without blocking signal tracks.This arrangement also provides a highly uniform local layoutenvironment, eliminating complex layout dependent device variabilitythat has become a substantial performance detractor in advancedtechnology nodes. Using unit cells with equal width as well as thecommonly used equal height allows logic functions which require moretransistors than are available in the single transistor track wide stackto be composed by optimally abutting unit cells either vertically orhorizontally, providing a critical degree of freedom in simplifying wireshapes.

FIG. 1 is an illustration of a top-down view of an example unit cell 100with which the principles of this disclosure can be embodied. The cellview of FIG. 1 depicts an accessible surface 105 of unit cell 100 acrosswhich a plurality of cell contacts 130 a-130 j, representativelyreferred to herein as cell contact(s) 130, are disposed. Each cellcontact 130 is electrically connected to a node of cell circuitryconstructed beneath accessible surface 105. For example, unit cell 100may comprise a double stack of complementary field-effect transistor(CFET) circuits, i.e., two pairs of common gate n-type and p-typetransistor pairs stacked one atop another in what is referred to hereinas an active device stack. An example of such an active device stack isillustrated in FIG. 2. In the example embodiment of FIG. 1, such adevice stack may be confined to a 4 track (4T) tall, as illustrated bytracks 140 a-140 d, representatively referred to herein as track(s) 140,and 2 cpp wide cell, as indicated in FIG. 1. In such a double stackconfiguration, four (4) active channels may be established in respectiveactive regions 150 and controlled by way of voltages applied to andinterconnections established across cell contacts 130, where, forexample, cell contacts 130 a and 130 c may be connected to the bottomp-diffusion layer, cell contacts 130 d and 130 e may be connected to thetop p-diffusion layer, cell contacts 130 f and 130 g may be connected tothe top n-diffusion layer, cell contacts 130 h and 130 j may beconnected to the bottom n-diffusion layer and cell contacts 130 b and130 i may be connected to common polysilicon gates of the upper andlower CFET pairs, respectively. One may also view these contacts asfollows: cell contacts 130 a and 130 c may serve as source and draincontacts for a p-type transistor of a lower CFET pair, cell contacts 130d and 130 e may serve as source and drain contacts for a p-typetransistor of an upper CFET pair, cell contacts 130 f and 130 g mayserve as source and drain contacts for an n-type transistor of the upperCFET pair, 130 h and 130 j may serve as source and drain contacts for ann-type transistor of the lower CFET pair and cell contacts 130 b and 130i may serve as common gate contacts to the upper and lower CFET pairs.This contact assignment is not essential to practicing the inventiveconcept described herein; other contact assignments are possible and maydepend on the interior architecture of the unit cell.

In addition to cell contacts 130, accessible surface 105 further exposesupper surfaces of a VDD power wall 110 and a VSS power wall 120. Incertain embodiments, VDD power wall 110 and VSS power wall 120 areconstructed as walls extending upward from the substrate surface toaccessible surface 105. Accordingly, VDD power wall 110 and VSS powerwall 120 are accessible to local interconnects interior to unit cell 100as well as to wiring at accessible surface 105. Accordingly, such localinterconnects may connect directly to VDD power wall 110 and/or VSSpower wall 120, such as for transistor biasing, as opposed to makingsuch connection at accessible surface 105. In certain embodiments, VDDpower wall 110 and VSS power wall 120 may each be situated in the spaceof a single diffusion break and, as illustrated in FIG. 1, may eachtraverse cell boundaries so as to be available to adjacent cells.

Also illustrated in FIG. 1 are active regions 150 of which there arefour (4) in exemplary unit cell 100. However, it is to be understood thefour active regions may each comprise multiple channels in which currentflows from source to drain (or vice-versa). For example, each activeregion 150 may comprise multiple current-carrying components, e.g.,nanowires or nanosheets, in a gate-all-around (GAA) configuration. Otheractive regions may also be realized in embodiments of the invention,usually depending on the technology node of which the unit cell isdesigned and manufactured.

FIG. 2, which comprises FIGS. 2A-2E, is a diagram revealing theinternal, 3D structure of unit cell 100 through several cross-sectionalviews. The different views are depicted in FIGS. 2A-2D and arereferenced to FIG. 2E, which illustrates the accessible surface 105 andcell contacts 130 depicted in and described with reference to FIG. 1. Itis to be understood that FIG. 2, including FIGS. 2A-2E, is a schematicillustration and is not drawn to scale.

FIG. 2A represents a cut through bottom local interconnect 215, whichmay connect cell contact 130 a to a source/drain of the lower-mosttransistor 210 a in active device stack 250, local interconnect 235,which may connect cell contact 130 c to a drain/source of the lower-mosttransistor 210 a in active device stack 250, and a top gate polysiliconinterconnect 230, which may connect cell contact 130 b to the commongate of the upper-most CFET pair comprising transistors 210 c and 210 d.It is to be noted that, in certain embodiments, VDD power wall 110 andVSS power wall 120 may be connected to buried power rails,representatively illustrated at buried power rails 112 and 122,respectively, as well as being exposed at upper surfaces thereof onaccessible surface 105.

FIG. 2B represents a cut through local interconnect 215, localinterconnect 220, which may connect cell contact 130 f to a drain/sourceof transistor 210 c in active device stack 250, local interconnect 225,which may connect cell contact 130 h to a source/drain of transistor 210c of active device stack 250 and cell contact 130 d, which may bedirectly connected to source/drain of upper-most transistor 210 d ofactive device stack 250. Additionally, FIG. 2B represents a cut througha portion of active device stack 250.

FIG. 2C represents a cut through common gates in active device stack250. Each of the upper and lower CFET pairs may be connected torespective cell contacts 130 b and 130 i through polysiliconinterconnects 230 and 240.

FIG. 2D represents a cut through local interconnect 225, which mayconnect cell contact 130 a to a source/drain of the lower-mosttransistor 210 a in active device stack 250, interconnect 245, which mayconnect cell contact 130 j to a drain/source of the upper-mosttransistor 210 d in active device stack 250, and a bottom gatepolysilicon interconnect 240, which may connect cell contact 130 i tothe common gate of the lower-most CFET pair comprising transistors 210 aand 210 b.

According to embodiments of the inventive concept disclosed herein,signal and power connections may be routed on a plane above activedevice stack 250, e.g., on accessible surface 105, to be functionalizedin local conductive wiring on what is referred to herein as afunctionalization layer. Local power rails may be run in the space of asingle diffusion break. Accordingly, each unit cell can have uniformdimensions and can optionally have uniform geometry includingtransistor, gates, and local interconnects.

FIG. 3A is an illustration of a 10×10 array 300 of unit cells tohighlight the regularity of the front end-of-line (FEOL) and middleend-of-line (MEOL) layouts. For purposes of identification, each cell inarray 300 is associated in FIG. 3A with a column and row identifier,e.g., unit cell 3F refers to the unit cell in column 3 and row F ofarray 300. It should be observed that, insofar as FEOL and MEOL layoutsare concerned, array 300 is highly regular and, as such, variousmanufacturing processes can be leveraged to simplify overallmanufacturing efforts and decrease costs. In certain embodiments, array300 may be a monolithic integrated circuit, wherein the unit cells areall constructed on a single substrate (not illustrated).

FIG. 3B is an illustration of unit cell array 300 in which only theactive channel regions, representatively illustrated at active channelregion 310, and source/drain contacts, representatively illustrated atsource/drain contact 320. FIG. 3B highlights the possible use oflow-cost frequency multiplication patterning techniques (e.g., directedself-assembly or self-aligned multiple patterning, e.g., self-aligneddouble/triple/quadruple patterning to image these critical features.

FIG. 3C is an illustration of unit cell array 300 in which a grid ofcut-masks, representatively illustrated at cut-masks 330 a and 330 b,are depicted that can optionally provide a low cost, high precisionsolution to form line-ends for local interconnects and poly gates.

FIG. 3D is an illustration of unit cell array 300 in which VDD powerrails, representatively illustrated at VDD power rail 340, and VSS powerrails, representatively illustrated at VSS power rail 350, are depicted.It is to be understood that these power rails are positioned in thespace left by diffusion breaks. Also, illustrated in FIG. 3D, aremacro-level power rails, representatively illustrated at macro-levelpower rail 360, that supply power to the local power rails.

FIG. 4 is an illustration of a top-down view of a unit cell 400 that hasundergone functionalization via back-end of line (BEOL) processes. Unitcell 400 may possess the same internal architecture as unit cell 100described above. The cell contacts, representatively illustrated at cellcontact 403, may be distributed across accessible surface 401 so as toconnect to the same internal circuitry nodes to which like-positionedcell contacts 130 of unit cell 100 are connected. In the exampleillustrated, first metal 415 and second metal 420 are disposed overaccessible surface 401 so as to connect target-specific cell contacts403 and form thereby a specific logic cell, which, in the case of FIG.4, is a two finger inverter (INV2). In this example embodiment, threelevels of highly regularized and unidirectional metal connections areused. First, VDD power taps 430 a and 430 b and VSS power taps 460 a and460 b may connect specific source/drain contacts to the localpower-rail, i.e., VDD power rail 425 and VSS power rail 455. On aseparate layer of local wiring, vertically-aligned source/drain and/orgate contacts may be connected by 1^(st) metal, representativelyillustrated at 1^(st) metal connection 415. In yet another layer oflocal wiring, input/output pins of the logic cell, e.g., top gatecontact 405 as electrically connected to bottom gate contact 445 servingas the logic cell input pin, cell contact 440 serving as an n-typeoutput pin and cell contact 450 serving as a p-type output pin, may beconstructed via 2^(nd) metal, representatively illustrated at 2^(nd)metal connection 420, to which a circuit router can connect othercircuit components. In certain embodiments, a signal via,representatively illustrated at 410, may be constructed to connect aninput pin attached to 2^(nd) metal disposed horizontally acrossaccessible surface 401 to local wiring of 1^(st) metal disposedvertically across accessible surface 401.

FIG. 5 is an illustration of a top-down view of a pair of unit cells 505a and 505 b, each of which can be constructed identically to unit cell100 of FIGS. 1 and 2, as functionalized into a two input and-or-invert(AOI22) logic cell 500. With similarity to FIG. 4, 1^(st) metalconnections, representatively illustrated at 1^(st) metal connection515, are directed vertically and 2^(nd) metal connections,representatively illustrated at 2^(nd) metal connection 520, aredirected horizontally, with power taps, representatively illustrated atpower tap 525, being placed as needed. The illustrated embodiment ofFIG. 5 demonstrates the efficient use of 1^(st) metal connection 510 tostrap the output of p-type “A” transistors to the input of p-type “B”transistors in a vertical cell abutment to form the AOI22 logic cell500.

FIG. 6 is an illustration of a top-down view of a pair of unit cells 605a and 605 b, each of which can be constructed identically to unit cell100 of FIGS. 1 and 2, as functionalized into a two input and (AND2)logic cell 600, essentially a two input not-and circuit (NAND2 in unitcell 605 a) connected to a dual-output inverter circuit (INV2 in unitcell 605 b). With similarity to FIG. 4, 1^(st) metal connections,representatively illustrated at 1^(st) metal connection 615, aredirected vertically and 2^(nd) metal connections, representativelyillustrated at 2^(nd) metal connection 620, are directed horizontally,with power taps, representatively illustrated at power tap 625, beingplaced as needed. The illustrated embodiment of FIG. 6 demonstrates theefficient use of 2^(nd) metal connection 610 to strap the output of theNAND2 circuit to the gate of the INV2 circuit in a horizontal abutmentto form the AND2 logic cell 600.

FIG. 7 is an illustration of a top-down view of a pair of unit cells 705a and 705 b, each of which having a single CFET pair in their respectiveactive device stacks as opposed to two CFET pairs of the embodiment ofFIGS. 1 and 2. FIG. 7 demonstrates how the design methodology describedherein can be applied to other 3Di approaches. In the illustratedembodiment of FIG. 7, a two input not-and (NAND2) logic cell 700 isconstructed by way of functionalization techniques similar to thosedescribed above.

Table 1 shows sample area scaling achieved with techniques hereincompared to a relatively aggressive 5T 2D design. Note that the scalingfactors show a significant scaling benefit provided by techniquesherein.

TABLE 1 Cell 2D Size 3D Size Scale Factor AOI22 5cpp × 5T = 25 2ccp × 4T× 2 = 16 16/25 = 0.64 NAND2 3cpp × 5T = 15 2cpp × 4T = 8  8/15 = 0.53AND 5cpp × 5T = 25 4cpp × 4T = 16 16/25 = 0.64 INV2 3cpp × 5T = 15 2cpp× 4T = 8  8/15 = 0.53

Embodiments of the inventive concepts described herein can include anintegrated circuit or semiconductor device with an array of uniform unitcells. A fixed footprint (width and height) unit cell contains all frontend-of-line (FEOL, e.g., device, source/drain, gate) and middleend-of-line (MEOL, e.g., local interconnect) constructs. A uniform andfixed-pitch array of contacts may be provided to route all signal andpower connections to an accessible plane above the device stack. A setof local power rails running parallel to the polysilicon gateconnections may use the space of diffusion breaks. Logic synthesis canbe realized by abutting unit cells either horizontally (i.e., forming awide standard logic cell) or vertically (i.e., forming a tall standardlogic cell). A set of regular and unidirectional metal shapes may beused to functionalize the unit cells either into standard cell logic orfor large block synthesis (e.g., mapping large logic blocks into localwiring of an array of unit cells).

In the preceding description, specific details have been set forth, suchas a particular geometry and descriptions of various components andprocesses used to construct such components. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

Of course, the order of discussion of the different steps as describedherein has been presented for clarity sake. In general, these steps canbe performed in any suitable order. Additionally, although each of thedifferent features, techniques, configurations, etc., herein may bediscussed in different places of this disclosure, it is intended thateach of the concepts can be executed independently of each other or incombination with each other. Accordingly, the present invention can beembodied and viewed in many different ways.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,reticle, or a layer on or overlying a base substrate structure such as athin film. Thus, substrate is not limited to any particular basestructure, underlying layer or overlying layer, patterned orun-patterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description may reference particular types of substrates, but thisis for illustrative purposes only.

The descriptions above are intended to illustrate possibleimplementations of the present inventive concept and are notrestrictive. Many variations, modifications and alternatives will becomeapparent to the skilled artisan upon review of this disclosure. Forexample, components equivalent to those shown and described may besubstituted therefor, elements and methods individually described may becombined, and elements described as discrete may be distributed acrossmany components. The scope of the invention should therefore bedetermined not with reference to the description above, but withreference to the appended claims, along with their full range ofequivalents.

The invention claimed is:
 1. An integrated circuit comprising: unitcells arranged in an array, each unit cell comprising: field effecttransistors arranged in a stack; local interconnect structurescomprising select conductive paths between select terminals of the fieldeffect transistors to define cell circuitry that is confined within theunit cell; and an array of contacts disposed on an accessible surface ofthe unit cell, each contact being electrically coupled to acorresponding electrical node of the cell circuitry, wherein: the unitcells have a common footprint and are positioned in the array so thatdiffusion breaks embracing the cell circuitry of each unit cell alignwith the diffusion breaks in adjacent unit cells to form continuousspaces that extend across all unit cells in respective columns of thearray, and the integrated circuit further comprising power wallsdisposed in the continuous spaces, the power walls providing electricalpower to at least the unit cells in the respective columns of the array.2. The integrated circuit of claim 1, further comprising afunctionalization layer comprising electrically conductive wiringsegments formed between select contacts on respective accessiblesurfaces of one or more unit cells in the array.
 3. The integratedcircuit of claim 1, wherein upper surfaces of the power walls areexposed on the accessible surface of each unit cell in the respectivecolumns of the array.
 4. The integrated circuit of claim 1, whereinlower surfaces of the respective power walls are connected to buriedpower rails.
 5. The integrated circuit of claim 1, wherein the cellcircuitry is identical across all unit cells in the array.
 6. Theintegrated circuit of claim 5, wherein the cell circuitry is constructedfrom front end-of-line and middle end-of-line structures that extendacross the unit cells.
 7. The integrated circuit of claim 6, wherein thefront-end of line and middle-end of line processes includemultiplication patterning processes.
 8. The integrated circuit of claim7, wherein the multiplication patterning processes include directedself-assembly and/or self-aligned double patterning.
 9. The integratedcircuit of claim 1, wherein the field effect transistors are stacked incomplementary pairs.
 10. The integrated circuit of claim 9, whereingates of each of the complementary pairs of field effect transistors areelectrically connected to one another.
 11. The integrated circuit ofclaim 10, wherein the complementary pairs in the stack of field effecttransistors is greater than one in number.
 12. The integrated circuit ofclaim 1, wherein the field effect transistors are stacked in planes thatare parallel to the accessible surface.
 13. The integrated circuit ofclaim 1, wherein the integrated circuit is monolithic.
 14. An integratedcircuit comprising: electrical contacts disposed across a surfacebeneath which identical unit cells are constructed, each unit cellcomprising: transistors arranged in a stack, and local interconnectstructures comprising select conductive paths between select terminalsof the transistors to define cell circuitry that is confined within theunit cell, wherein select nodes of the cell circuitry are connected tothe electrical contacts disposed over the stack of transistors of eachunit cell; and power walls disposed in continuous spaces between groupsof the unit cells, the power walls providing electrical power to atleast the unit cells in the corresponding group thereof.
 15. Theintegrated circuit of claim 14, further comprising a functionalizationlayer including electrically conductive wiring segments formed betweenselect ones of the electrical contacts.
 16. The integrated circuit ofclaim 14, wherein select ones of the local interconnect structures areconnected to at least one of the power walls.
 17. The integrated circuitof claim 14, wherein the transistors are stacked in planes that areparallel to the surface on which the electrical contacts are disposed.